$s = '0123456789';
printf "%x\n", unpack 'Q', pack 'P', $s
    while $s =~ /\G./g;

# 55fd180fcc60
# 55fd18107f30
# 55fd18107ed0
# 55fd180e6700
# 55fd180fcc60
# 55fd18107f30
# 55fd18107ed0
# 55fd180e6700
# 55fd180fcc60
# 55fd18107f30

[download]

Looks like patterns don't matter, both between slashes (the above is for illusion of being useful, supposedly performed daily by thousands) and alternation of addresses, it just picks what's available.

use strict;
use warnings;
use feature 'say';
use Config;

say "$^V / $Config{ archname }";

for my $len ( 1e4, 1e5, 1e6, 1e7 ) {
    my $s = 'a' x $len;

    my %h;
    my @before = times;
    $s =~ /\G./gs and ++ $h{ pack 'P', $s } 
        for 1 .. $len / 100;                    # do just 1% !!!
    my @after = times;

    printf "Length: %8d, addresses: %6d, user: %6g, system: %6g\n",
        $len, scalar( keys %h ), 
        $after[ 0 ] - $before[ 0 ],
        $after[ 1 ] - $before[ 1 ]
}

__END__

v5.40.3 / x86_64-linux-thread-multi
Length:    10000, addresses:      1, user:      0, system:      0
Length:   100000, addresses:      1, user:      0, system:      0
Length:  1000000, addresses:      1, user:   0.01, system:      0
Length: 10000000, addresses:      1, user:   0.02, system:      0

v5.42.0 / x86_64-linux-thread-multi
Length:    10000, addresses:      2, user:      0, system:      0
Length:   100000, addresses:      3, user:   0.01, system:      0
Length:  1000000, addresses:      3, user:   0.39, system:      0
Length: 10000000, addresses:      3, user: 139.87, system:      0

v5.43.8 / x86_64-linux
Length:    10000, addresses:      2, user:      0, system:      0
Length:   100000, addresses:      3, user:   0.01, system:      0
Length:  1000000, addresses:      3, user:   0.38, system:      0
Length: 10000000, addresses:      3, user: 138.75, system:   0.01

v5.42.0 / MSWin32-x64-multi-thread
Length:    10000, addresses:      2, user:      0, system:      0
Length:   100000, addresses:      2, user:      0, system:      0
Length:  1000000, addresses:      2, user:  0.844, system:  1.063
Length: 10000000, addresses:     70, user: 154.453, system: 253.812

[download]

It's much worse on Windows, with absurdly grotesque "system" time (I understand it's approximation for that OS); I can only assume buffers, when long enough (?), are continuously requested to be de-allocated and allocated, from OS, again and again, which is not the case with Perl on Linux.

If there's a bug it's a shock it goes unnoticed, I'm just a no-one. In fact I'm grateful that yesterday it wasn't possible to post, I now see the above is separate from another similar issue from 5.20 and on; better not to mix them together

In reply to 5.42: Does m// toss a string around? by Anonymous Monk

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